Cool -- a paper that contradicts the assumption central to my Master's thesis

The observation central to this work is: there are lots of channels on Venus but if you look at the topography along them, they don't go from uphill to downhill; they undulate a lot. The assumption I used in my thesis was one first suggested by Goro Komatsu and Vic Baker: that the channels could be used as a marker of paleo-flatness, so you could learn something about what's happened in Venus tectonics since the channels formed by examining how topography along channels differs from flatness. This paper says, no, the channels formed that way, because they didn't form on the surface, they formed below the surface at the interface between the plains lavas and some other layer.

I'll be very curious to see if they present this at this year's Lunar and Planetary Science Conference and what the other people in the Venus community think about it. But it may be hard to get an unbiased opinion. Vicki Hansen (second author on this paper, the first author is very likely a Ph.D. student of hers) has long represented one polar extreme in an extremely, nastily polarized debate about how to interpret geology from Magellan SAR images; the other pole was occupied by my graduate advisor, Jim Head, and his coworker Alexander ("Sasha") Basilevsky. After witnessing one particularly ugly and non-constructive debate between these two poles at an LPSC meeting, one of my fellow students (Geoff Collins, now a professor at Wheaton) summed up their debate: "I feel like Sasha is arguing 'Can't you see the forests around you?' while Vicki is shouting 'No, no! There are only trees!'"

Cool -- a paper that contradicts the assumption central to my Master's thesis

--Emily

Emily, how did you decide to choose this topic for your thesis? Is it available online? Thank you.

This does explain your image symbol, at least.

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"After having some business dealings with men, I am occasionally chagrined, and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

Emily, how did you decide to choose this topic for your thesis? Is it available online? Thank you.

I went to my archives, blew the dust off the CDs, and uploaded the text and figures to a site where you can download them if you really care. It wasn't ever finished far enough to be ready to be submitted for publication, though it was being formatted as a JGR paper, so it's very much a draft, but have at it! It's not doing anybody any good not being read. It's questionable though whether it will do anybody any good being read -- it's only been "peer reviewed" by my advisors.

The topic was suggested by my advisor. I did the mapping work with Jim and Sasha (though I had to teach myself how to do the GIS stuff with lots of help from various tech support people), then there's a whole section on geophysics that I did with Marc Parmentier.

The observation central to this work is: there are lots of channels on Venus but if you look at the topography along them, they don't go from uphill to downhill; they undulate a lot. The assumption I used in my thesis was one first suggested by Goro Komatsu and Vic Baker: that the channels could be used as a marker of paleo-flatness, so you could learn something about what's happened in Venus tectonics since the channels formed by examining how topography along channels differs from flatness. This paper says, no, the channels formed that way, because they didn't form on the surface, they formed below the surface at the interface between the plains lavas and some other layer.

Although different mechanisms and processes are involved, there are interesting parallels with similar debates regarding Mars' ancient valley networks.

Although different mechanisms and processes are involved, there are interesting parallels with similar debates regarding Mars' ancient valley networks.

Huh. I didn't know that -- do you mean that people are talking about a subsurface (or maybe subglacial) formation mechanism for the valley networks? I'd be shocked and amazed if Komatsu and Baker weren't also involved in these studies -- they've cornered the market on planetary channels.

Huh. I didn't know that -- do you mean that people are talking about a subsurface (or maybe subglacial) formation mechanism for the valley networks?

Sure. For example, there are numerous papers on a groundwater sapping origin for Mars' ancient valley networks. Just off the top of my head: Goldspiel and Squyres [2000].

EDIT: You might be aware of a special issue of the journal Geomorphology entitled, appropriately enough, "Extraterrestrial geomorphology." The papers, published in 2001 but undoubtedly prepared before that, are a bit dated, though.

Huh. I didn't know that -- do you mean that people are talking about a subsurface (or maybe subglacial) formation mechanism for the valley networks? I'd be shocked and amazed if Komatsu and Baker weren't also involved in these studies -- they've cornered the market on planetary channels.

--Emily

Emily:

Well, Baker likes floods. Big floods. Reallllllly big floods!

So maybe sub-glacial channels wouldn't have the same, er, flush of enthusiasm...

Emily, Are there any lakes, or lake shorelines, along the valley? I would assume for such a long valley that there was one point somewhere where it hit a local minimum and created a lake of "whatever".

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Space Enthusiast Richard Hendricks --"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C ClarkeMother Nature is the final inspector of all quality.

Actually, Mars scientists seem to have always preferred groundwater sapping to surface runoff as a formation mechanism for the valley networks -- although some of them in turn believe that precipitation (either rain or snowmelt) in high regions may have trickled locally underground to start the sapping in the first place, and some believe that there is evidence for BOTH mechanisms, perhaps at different times in Martian history.

The thing about sapping is that it can work using a much smaller total amount of liquid water. It's very easy to visualize an ancient Mars which gradually chilled down and developed a steadily thickening surface layer of permafrost, replacing surface runoff with underground liquid-water sapping at greater and greater depths until the process shut off completely save in the few remaining regions of geothermal activity.

Michael Carr has quite a bit on this subject in his extremely useful 1995 book "Water on Mars" (which I recommend to non-scientists as well as scientists -- it's thorough but remarkably easy to understand). He was a major proponent of sapping at the time, and I believe still is. The question is whether the extreme shortage of visible tributaries in the Martian valley networks is due to an actual original lack of them -- as would be the case from sapping -- or whether the erosion and aeolian soil movement that's gone on in the billions of years since then has just covered up a lot of the initial little tributaries that you'd get from surface runoff. (This is one reason why a Martian SAR orbiter would still be useful scientifically to punch through the upper few meters of loose soil.)

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